This invention relates to service-observing equipment and, more particularly, to an arrangement for automatically verifying the type of usage occurring on any trunk in a switching office without knowing in advance the trunk group within which such usage is likely to occur.
Service-observing equipment has long been available which could be wired to a group of lines or trunks that the telephone company believed would be likely to exhibit certain characteristics. For example, if a particular frame seemed to exhibit a high incidence of trouble conditions, the service-observing equipment could be wired to monitor the particular groups of lines, trunks or registers associated with that frame. The service-observing equipment would be called into operation whenever one of the group of circuits appearing in the designated frame was sized for use.
It has also been possible, heretofore, to condition a call data recording system to match on the number of a predetermined line incident to the arrival of a call placed by that line at a tandem switching center. An example of an automatic message accounting (AMA) system having such service-observing equipment is found in FIGS. 120 through 132 of R. N. Breed et al. U.S. Pat. No. 2,848,543 issued Aug. 19, 1958 and described at columns 114-118 therein. In the performance of its principal operation, the Breed et al. patent system employs wholly electromechanical relay circuitry and punched paper tape recorders.
More recently, an improvement has been made to the call data recording system disclosed in the aforementioned Breed et al. patent according to which the punched paper tape recorders have been replaced by a minicomputer-controlled magnetic tape recording apparatus that employs scanners to monitor continuously the supervisory states of the calling and called sides of the trunks in the office. The sequence of signal states observed by the scanner, e.g., at the calling side sleeve lead and at a contact of the called side supervisory ("CS") relay, is forwarded to a minicompuuter and therein analyzed in conjunction with the automatic message accounting information read by the scanner from the AMA recorder leads. Details of typical AMA recorder lead circuitry are disclosed in W. W. Carpenter U.S. Pat. No. 2,688,658 issued Sept. 7, 1954. From the combination of trunk state and AMA record lead information, the minicomputer is able to provide assembled recordings of call charge information so that customers may be properly billed for their calls.
In implementing the "computerized" version of the Breed et al. patent system, however, certain aspects of the service-observing problem remained to be solved. To definitely classify the actual usage being made of the transmission path, observation of the transmission path itself is required. Heretofore, actual connection to the transmission path has been severely limited because it is not desired to interfere with the privacy of customers' communications. Thus, while the computer of the aforementioned system is eminently well-suited to accept data from sleeve lead and relay contact scan points, and to compute the differences in times between signal states detected by the scanner, and to multiply the computed times by charge rates, the computer itself cannot verify the actual type of usage being made of the tip-and-ring conductors because it is not given access to these conductors.
In addition to the foregoing systems, automatic equipment has been available in the prior art for sequentially performing tests on the transmission paths of all of the trunks appearing in a switching office. In keeping with the policy of maintaining the privacy of customers' communications, such equipment has included busy/idle testing circuitry which functioned to preclude attachment of the test equipment to the tip-and-ring path if the trunk was found to be busy when it was reached in the sequence of test progression. (See for example, pp. 223-226 of the June 1956 issue of the Bell Laboratories Record containing an article entitled "CAMA -- Automatic Trunk-Test Circuit" and col. 6, lines 34-38 and col. 11, lines 5-63 of Short et al. U.S. Pat. No. 3,829,627 issued Aug. 13, 1974).
While the telephone companies wish to maintain the goal of keeping customers' conversations secure against unauthorized eavesdropping, the companies have noticed increased use of the switching network in recent years by unscrupulous persons. With the great reductions in the cost of electronic equipment, some persons have fabricated equipment to simulate switching control signals employed in the direct distance dialing network and have placed toll calls in such a manner as to defeat the automatic message accounting equipment. The result of such fraudulent use is to increase the costs of legitimate rate payers. Yet, it would not be feasible to have telephone company personnel monitor the tip-and-ring conductors of every telephone line, or even continuously to monitor the tip-and-ring conductors of lines suspected of having an inordinate number of unpaid toll calls. Accordingly, the need has been perceived for automatic apparatus which could monitor any of the trunks in a telephone office and directly ascertain the character of the transmission path usage.